How to register keymaps for all editor types?
I randomly discovered the answer to my question on the Blender Python API Documentation

My registration code now looks like this:

addon_keymaps = []
def register_keymaps():
    wm = bpy.context.window_manager
    km = wm.keyconfigs.addon.keymaps.new(name = "Window",space_type='EMPTY', region_type='WINDOW')
    kmi = km.keymap_items.new("wm.call_menu_pie", type = "E",alt=True, value = "PRESS")
    kmi.properties.name = "editor_switcher_pie_menu"
    addon_keymaps.append(km)


You can find the final version of my addon on GitHub